1. Field of the Invention
Embodiments of the present invention relate generally to the storage and retrieval of data within a magnetic recording medium. In particular, embodiments of the present invention relate to the structure of a main pole of a magnetic head for perpendicular recording to control the domain lockup phenomenon and a process of manufacturing the main pole.
2. Related Art
One approach to increase the areal recording density of a magnetic recording medium is to use a perpendicular recording method, instead of the conventional longitudinal magnetic recording method. In magnetic perpendicular recording, a magnetic head is designed to direct magnetic flux through the recording layer of the magnetic recording medium in a direction which is generally perpendicular to the plane of the magnetic recording medium. Typically the magnetic recording medium for perpendicular recording has a hard magnetic recording layer and a magnetically soft underlayer. The perpendicular recording method offers an advantage in that microscopic recorded magnetization is thermally stable.
A magnetic head for perpendicular recording generally includes two portions, a write head portion or head for writing or programming magnetically-encoded information on the magnetic recording medium or disc and a reader portion for reading or retrieving the stored information from the magnetic recording medium.
The write head or recording head in a disc drive using a perpendicular recording method typically includes a main pole and a return pole which are magnetically separated from each other at an air bearing surface (ABS) of the writer by a nonmagnetic gap layer, and which are magnetically connected to each other at a region away from the ABS at a back gap closure reading called a yoke. In FIG. 1, an angled side view of a portion 10 of a perpendicular recording head is shown to include a main pole 12, a coil(s) 14 and a return pole 16. The main pole 12 and the return pole 16 form a U-shape around the coil 14. In operation, current flows through the coil 14 creating a magnetic field between the main pole 12 and the return pole 14. When programming or storing information onto a magnetic recording medium, magnetically-encoded information is written by creating a magnetic path from the main pole 12 to the medium and back to the return pole 16 to close the loop.
This structure is a single-pole write head because, while a main pole and return pole are referred thereto, the return pole is not physically a pole. Rather, the return pole serves to close the loop with the main pole through the soft underlayer of the magnetic recording medium.
To write data to the magnetic recording medium, an electrical current is caused to flow through the conductive coil 14, thereby inducing a magnetic field across the gap between the main pole 12 and return pole 16. Both the main pole 12 and return pole 16 generate a magnetic field in the magnetic recording medium during recording when the write current is applied to the coils 14. A magnetic moment of the main pole 12 should be oriented along an easy axis parallel to the ABS without a write current field from the write coils 14.
When the magnetic moment does not return to an orientation parallel to the ABS after being subjected to multiple instances of the write current field, the main pole 12 is not stable. Therefore, in an unstable pole, the orientation of the magnetic moment might remain nonparallel to the ABS position even after current to the write coils 14 is turned off. A moment that exists in the absence of a magnetic field is referred to as a remnant moment. The domain pole lockup phenomenon is created when there is a remnant moment in the perpendicular direction. Accordingly, the remnant magnetic field of the main pole 12 may cause erase-after-write or undesirable erasure of information from the magnetic recording medium.
Generally, the narrower the main pole 12, the more bits can be written per unit area on to a medium. However, use of a narrow main pole has been known to introduce a large shape anisotropy, which can cause pole lockup and undesired erasure of valid data stored in the medium.
FIG. 2 shows an example of a single narrow main pole at 18. Shape anisotropy itself dictates the easy axis of magnetization to be along the long direction as indicated by 20. In high density recording, such as perpendicular recorders or heads, a narrow main pole 12 is preferable, such as that shown in FIG. 2, however, as stated earlier, the problem then becomes undesirable erasure due to the possible presence of a large remnant field. Thus, when programming or writing is performed and the head is shut off or not being employed for storage, the effects of a remnant field or a residual field preside.
One conventional technique for reducing the remnant moment of the narrow pole is to laminate the pole (which is made of a high moment magnetic material such as cobolt-iron) into multiple layers. The most recent lamination scheme utilizes anti-ferromagnetic coupling (AFC) between layers. The drawback with the AFC lamination schemes is that they are complicated and difficult to manufacture.
Thus, the need arises for improvements to the structure of the main pole of a perpendicular recorder or write head that effectuates low remnant magnetization to alleviate the pole lockup phenomenon that is simple in construction and does not increase the overall size of the recording device.